This invention relates to silicone pressure sensitive adhesive compositions. More particularly this invention relates to pressure sensitive adhesive compositions obtained by reacting a mixture comprising a polydiorganosiloxane, a silicone resin copolymer, a condensation catalyst, and at least one solvent or plasticizer having a boiling point of at least 200.degree. C. to form a reaction product, and then adding an organic peroxide or azo compound to the reaction product.
Silicone pressure sensitive adhesives (PSA's) are typically produced by either blending or condensing together a silicone resin and a silicone polymer. These types of silicone pressure sensitive adhesives have been disclosed for example in U.S. Pat. Nos. 2,736,721, 2,814,601, 2,857,356, and 3,528,940.
Silicone pressure sensitive adhesives which are produced by adding an amine or a salt of an amine to the silicone resin-silicone polymer blend have been disclosed for example in Great Britain Patent Specification No. 998,232. Silicone pressure sensitive adhesives have also been disclosed which comprise a resin, a polydiorganosiloxane fluid, and a condensation catalyst such as a metal salt of a carboxylic acid for example in U.S. Pat. No. 4,831,070.
European Patent Application No. 0459292 discloses a silicone pressure sensitive adhesive composition comprising a mixture two different pressure sensitive adhesive compositions containing resin and polymer blends.
U.S. Pat. No. 5,248,739 to Schmidt et al. discloses a silicone pressure sensitive adhesive composition produced by mixing together a silicone resin and a polydiorganosiloxane polymer and that these compositions can further comprise an organic peroxide as a crosslinking agent when the polydiorganosiloxane polymer does not contain unsaturated groups.
Great Britain Patent Publication No. 2301829 discloses silicone pressure sensitive adhesive compositions comprising 100 parts of an organopolysiloxane having a viscosity of at least 500,000 centipoise at 25.degree. C., 60 to 300 parts of a silicone MQ resin, and 20 to 2500 parts of a linear or cyclic volatile organosiloxane fluid having a boiling point in the range of about 95.degree. C. to about 250.degree. C. where the organo radicals of the silicone PSA composition are selected from C.sub.1-13 organo radicals which are attached to silicon by carbon-silicon linkages and further discloses that the curing of the silicone PSA composition is by the use of a free-radical initiator such as an organic peroxide.
Conventional peroxide curable silicone pressure sensitive adhesives are typically supplied at 55 to 60% solids by weight in an organic (typically aromatic) solvent diluent. This is done to lower the viscosity of the film forming product, making it easier to handle and apply evenly to a desired substrate. These solvents typically boil at 100 to 140.degree. C., and care is taken to remove them prior to thermal activation by a peroxide initiator.